The double helix makes a complete turn in just over 10 nucleotide pairs, so each turn takes a little more (35.7 Å to be exact) than the 34 Å shown in the diagram.

There is an average of 25 hydrogen bonds within each complete turn of the double helix providing a stability of binding about as strong as what a covalent bond would provide.

The diameter of the helix is 20 Å.

The helix can be virtually any length; when fully stretched, some DNA molecules are as much as 5 cm (2 inches!) long.

The path taken by the two backbones forms a major (wider) groove (from "34 A" to the top of the arrow) and a minor (narrower) groove (the one below).

This structure of DNA was worked out by Francis Crick and James D. Watson in 1953. It revealed how DNA — the molecule that Avery had shown was the physical substance of the genes [Link] — could be replicated and so passed on from generation to generation. For this epochal work, they shared a Nobel Prize in 1962.